Hyperbilirubinemia (jaundice) is common in infants, and affects, in some degree, up to 50% of full-term infants, and most preterm infants. Bilirubin is the end result of chemical reactions involved in the breakdown of hemoglobin molecules. Bilirubin circulates through the blood stream chiefly in unconjugated form, and is processed by catalysis in the liver for conversion into a water-soluble form, which can then be excreted into the intestines as bile. The livers of newborn infants tend to have limited ability to process bilirubin, so infants are prone to accumulation of unconjugated bilirubin, and thus develop jaundice. In most cases, the jaundice is mild, and resolves spontaneously during the first week of life. However, jaundice is potentially dangerous, as high levels of bilirubin are toxic to brain tissue.
While the immaturity of liver cells is the chief cause of jaundice, there may be pathologic causes, which include h.ae butted.molytic anemia, polycythemia, extravasated blood, and even metabolic disorders. These pathologic causes can create sudden and severe onset of excess bilirubin levels. The goal of medical intervention is to mitigate or curtail the rise in bilirubin levels in the blood, to avoid a toxic accumulation. Approximately 10% of newborns require such intervention.
It is well known that, when infants are exposed to light in the blue region of the spectrum (410 to 460 nanometers or nm), a photochemical reaction takes place in the skin. The photochemical reaction changes unconjugated bilirubin into more soluble metabolites, including photobilirubin, which is then excreted into the bile, and if further photooxidation occurs prior to excretion, generates products which are excreted in the urine. Such phototherapy has proven to be an effective treatment for the vast majority of infants with unconjugated hyperbilirbinemia.
Infant phototherapy for jaundice is generally administered by phototherapy units, the effectiveness of which depend, at least in part, on the irradiance delivered by the light source, and the amount of skin exposed to the light. The light delivery systems in common use in hospital settings fall into two general categories, the first of which involves a crib-like structure for holding the infant, surmounted by banks of fluorescent or halogen lamps. These systems deliver light in the abovementioned blue region of the spectrum, at the target intensity of 5 to 9 .mu.W/cm.sup.2 /nm of bandwidth. This type of phototherapy unit has a number of disadvantages. First, the target light intensity is at a level at which retinal damage is of concern, and consequently the infant must wear protective eye patches. Secondly, to maximize the area exposed to the phototherapy, the infants must be essentially naked; since such infants have difficulty in temperature regulation, they must be maintained in temperature-controlled isolettes during phototherapy. Maintenance in temperature-controlled isolettes, in turn, tends to reduce the availability of human contact. The bulk and cost of the isolettes, in turn, tends to limit the use of this first type of phototherapy unit to hospital environments.
The second type of phototherapy unit which is generally available is the fiberoptic phototherapy blanket. This is a relatively flexible panel-like support for holding the ends of the fibers of one or more fiberoptic cables adjacent to a surface of the blanket, so that light propagating through the optical fibers is directed toward one side of the panel. This phototherapy blanket can be placed on the bottom of a conventional isolette, so that the infant can be illuminated from the bottom, as well as from the top by fluorescent or halogen lamps conventionally disposed. For infants with milder degrees of hyperbilirubinemia, the fiberoptic phototherapy blanket may be used alone, by wrapping the flexible panel about the infant's body, and securing the panel in place. Since the panel is opaque, there is less concern that the light can affect the infant's eyes, which tends to reduce the need for eye protection. If the panel is wrapped about the torso, the child can be dressed over the panel to keep it warm, and thus attains at least some mobility, which allows parental interaction, albeit limited by the "umbilical" optical fiber cable tethered to the light source. Since such phototherapy blanket units are relatively compact, they are more amenable to home use than the more conventional phototherapy "cribs". The ability to provide home therapy for mild cases of jaundice tends to reduce healthcare costs by eliminating the need for hospitalization in all but severe cases of jaundice.
Improved phototherapy devices and methods are desired.